Reports have claimed inspectors from the country's Policia Judiciaria were exploring a new theory. Lisbon-based national newspaper Correio de Manha reports the organised Algarve-based crime group may have snatched the three-year-old from the Praia da Luz resort in the region in May 2007.
The claim emerged as British police announced they will disclose new information of their own which they uncovered during a separate review, named Operation Grange.
Details will be unveiled during a BBC Crimewatch appeal later this month. It will be first time Madeleine's parents, Glasgow-born Gerry McCann and his wife Kate, have faced the police who declared them suspects during their initial inquiries.
Assistant Commissioner Mark Rowley, of the Metropolitan Police, said: "There is new information not previously presented. Fresh, substantive material upon which to make an appeal.
"It's substantially different," he added. "It's not just a bland 'can you help us' appeal, there is some different material and a different understanding to be presented."
The McCanns' spokesman Clarence Mitchell said: "Kate and Gerry remain very grateful to the Met for the work they are doing in liaison with the Portuguese authorities.
"Their forthcoming appearance on Crimewatch is an important stage in that ongoing process. Naturally, they hope it will lead to information that will provide the breakthrough to finding Madeleine."
Officers working in Operation Grange have also confirmed that thousands of tourists staying in the area six years ago would be contacted by Scotland Yard in the near future.
British police have been searching through phone records of holidaymakers from more than 30 countries who were staying in the Algarve resort of when the three-year-old went missing.
Thousands of tourists are likely to receive a call, as the Metropolitan police continue their two-year inquire which has cost the public purse around £5 million.
The Metropolitan Police have issued requests to 31 countries asking local police to help identify those who may have been in the Praia da Luz area between April 28 and May 3, 2007.
Investigators hope to create an evidence log which may lead to new witnesses.
Detective Chief Inspector Andy Redwood, who is heading the review, claims they have unearthed "substantially different" material under the project named Operation Grange.
Mr Redwood said: "We are doing it the hard way quite frankly. This is not just a general trawl, this is a targeted attack in relation to that database to see if it assists us in finding out what happened to Madeleine McCann at that time.
"A lot of the focus is not necessarily to find a suspect, but also witnesses. We are trying to understand who was there for a range of reasons.
"If you were in Praia da Luz at the time, you may get a routine phone call from the police."
Portuguese police continue to cooperate with the British review, although they insist they will not officially reopen their own investigation.
Detectives working out of Faro will help Scotland Yard pursue 41 persons of interest who have been identified.
Fifteen of those suspects are British, although officers say they are close eliminating three individuals from their inquiries.
The operation has amassed 39,148 documents linked to the case.